bsdf henyeygreenstein(float anisotropic_bias, ...)
The Henyey-Greenstein function scatters light either forward or in reverse depending on the
anisotropic_bias provided to the function which must be a floating point value between -1 and 1. A value of 0 will cause isotropic scattering (identical to the
isotropic() bsdf) while positive values produce forward scattering and negative values produce reverse scattering. The extrema of -1 and 1 cause all light to be scattered in a single direction, back toward the light for -1 and without any directional change for 1.
No normal vector is required to construct a Henyey-Greenstein BSDF since it has no directionality. The default albedo for the BSDF is 1, which means it scatters 100% of the incoming light.